Indicator screen with controlled voltage to matrix crosspoints thereof

ABSTRACT

This invention provides an indicator screen comprised of two vertically superimposed systems of parallel transparent conductor paths, a nematic liquid crystalline layer positioned between the two conductor systems, and an interrupted barrier-free layer of a non-linear resistor material arranged between one of the conductor systems and the liquid crystalline layer.

OR 307301607 a i Q] I 1 f UIlitEd State W [111 3,730,607 Grabmaier etal. 1 May 1, 1973 [54] INDICATOR SCREEN WITH CONTROLLED VOLTAGE TOMATRIX [56] References Cited CROSSPOINTS THEREOF UNITED STATES PATENTS[75] Inventors: g ss: 2:22:33 iyzf ifig f i 3.322485 5/1967 Williams.350/160 LC Wolff Mumch' Ofgermany Primary ExaminerRonald L. Wibert [73]Assignee: Siemens Aktiengesellschaft, Berlin & Assislam CG a Mu i h,Germany AImrneyCarlton Hill et al.

[22] Filed: July 12,1971 57 [21] Appl. No.: 161,776

ABSTRACT This invention provides an indicator screen comprised of twovertically superimposed systems of parallel transparent conductor paths,a nematic liquid crystal- [30] Forelgn Apphcauon Pmmty Data line layerpositioned between the two conductor July 23 1970 Germany ..P 20 36665.8 s stems, and an interrupted barrier-free layer of a non-linearresistor material arranged between one of [52] U.S. Cl ..350/160 LC theconductor systems and the liquid crystalline layer. [51] Int. Cl ..G02f1/34 [58] Field of Search ..350/1 60 LC, 267 6 Clams 6 Drawmg Flgures IJ 1 I Ill I I SHEET 2 OF 3 VOLTAGE INVENTORS r f, a @f m d Q a5 5 M BYATTYS.

INDICATOR SCREEN WITH CONTROLLED VOLTAGE TO MATRIX CROSSPOINTS THEREOFBACKGROUND OF THE INVENTION l. Field of the Invention This inventionrelates to an indicator screen composed of two systems of paralleltransparent conductor paths having interposed between them a nematicliquid crystalline layer and an interrupted barrier-free layer of anon-linear resistor material arranged between one of the conductorsystems and the liquid crystalline layer.

2. Description of the Prior Art A liquid crystalline material isgenerally in a liquid state but in contrast to ordinary liquids hascertain crystalline properties. The liquid crystalline material may haveone and in some cases several interphases varying between the firmcrystalline state and the isotropic liquid state, e.g. smectic, nematicand chloesterinic mesophases.

Nematic crystalline liquids which have been used in conjunction withsystems of conductor paths in a picture screen and the like, have apreferred alignment of their molecules along their longitudinal axisover a large range which is dependent upon the position or arrangementof the liquid crystalline material in the picture screen. The moleculescan be aligned over even larger ranges with the assistance of magneticand electrical fields of high voltages, e.g., l,OOO volts percentimeter. The voltage can be applied in such a manner that the opticalaxis of the molecules is parallel to its field axis. If an electricvoltage is applied to a thin nematic liquid crystalline layer, a visiblechange of the optical properties of the layer will occur only when theelectric field strength has reached a certain threshold value. When thisthreshold value is exceeded, the diffraction index of the nematiccrystalline liquid becomes increasingly turbulent and the light whichpasses therethrough will become more strayed and diffused. Thelight-straying which is caused by the turbulence of nematic crystallineliquids is also referred to as dynamic light-straying. A plausibleexplanation of the dynamic light-straying is based on the so-calledswarm theory. That is, the theory of the flight of several planes ofmolecules in formation. According to the swarm theory, the molecules ofthe nematic crystalline liquid gather in swarms of about molecules. Themolecules lie parallel to one another within these swarms. The swarmthus obtains a permanent dipole moment. When an electric field isapplied to the nematic crystalline liquid, the swarms align with theirpermanent dipole moment in the field direction. Due to the angle whichis formed by the longitudinal axis of the molecules in the moleculardipole moment, the longitudinal axis of the molecules has a certaininclination with respect to the field direction. If during this swarmingmovement, ions were to be moved through such a molecule arrangementunder the effect of an electric field, a shearing force would be exertedonto the individual volume elements which would tend to turn thelongitudinal axis of the molecules in the direction of the ion flow. Inthis manner there results a steady interaction between the alignment ofthe dipoles under the effect of the electric field and the alignment ofthe molecules along their longitudinal axis according to the directionof movement of the ions. This interaction causes a dynamic anisotropy ofthe diffraction index and thus, the dynamic light-straying is caused asa final effect.

Because of the properties of the liquid crystals, a layer of a liquidcrystal can be utilized as a picture screen whereby the liquidcrystalline layer is moved differently into the straying state with thehelp of matrixshaped electrodes. Such a picture screen can be used inconjunction with glass plates which would be arranged on both sides ofthe liquid crystalline layer and each of which have a system of parallelconductor paths respectively arranged on their inner sides. With thisarrangement, the system of conductor paths of one glass plate standsvertically superimposed on the other system of conductor paths in theother glass plate. With this arrangement, if a voltage is applied to avertical conductor path of one system and a horizontal conductor path ofthe other system, an electric field will be created at the cross pointof such conductor paths and extend through the liquid crystalline layer.This extension of the electric field will change the current behavior ofthe illuminated liquid layer at a corresponding point therein and causethe layer to light up or glow at this corresponding point. However,there is a problem in this arrangement in that a similar though lesserlight-straying is produced at the other cross points along the conductorpaths and not only at the selected cross point.

In an attempt to eliminate this light-straying, a practice has beenestablished whereby diodes are arranged between the liquid crystallinelayer and the conductor paths of one of the conductor path systems. Thecost, however, for constructing such a screen is excessive since a diodehas to be provided for each matrix cross point. The cost of producingthis diode matrix is greater than that of all of the remaining elementsof the liquidcrystalline picture screen.

Accordingly, it is the primary object of the present invention toprovide a practical and economical means for producing a picture orindicator screen where the straying of light in response to anelectrical charge, to various electric cross points of the liquid matrixof the indicator or picture screen is eliminated.

Another object of the present invention is to provide a simple method ofproducing a liquid crystalline indicator or picture screen where thelight does not stray over the various cross points of its liquidcrystalline matrix.

SUMMARY OF THE INVENTION The present invention provides an indicatorscreen which overcomes the disadvantages of the prior art structures.The indicator screen of the present invention includes two verticallysuperimposed systems of parallel conductor paths, a nematic liquidcrystalline layer interposed between them, and an interruptedbarrier-free layer of a non-linear resistor material arranged betweenone of the conductor path systems and the liquid crystalline layer. Thenon-linear resistant material consists of an oxide layer, for example,an aluminum oxide layer. With such a layer of non-linear resistormaterial, the problem of light straying upon a voltage application tothe various cross point of the conductor paths is eliminated.

Other objects, features and advantages of the present invention will bereadily apparent from the following description of certain preferredembodiments thereof taken in conjunction with the accompanying drawingsalthough variations and modifications may be effected without departingfrom the spirit and scope of the novel concept of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a partial schematic view ofa conventional picture screen having a liquid crystalline layer;

FIG. 2 illustrates a substitute circuit diagram of the picture screenshown in FIG. 1;

FIG. 3 is a partial sectional view of an indicator; screen according tothe present invention illustrating an interrupted barrier-free layer ofa non-linear resistor material arranged inbetween a liquid crystallinelayer and a corresponding conductor path system;

FIG. 4 is a graph illustrating the current voltage characteristic of theinterrupted barrier-free layer of non-linear resistor material shown inFIG. 3;

FIG. 5 illustrates a substitute circuit diagram of the indicator screenof which a partial sectional view is shown in FIG. 3; and

FIG. 6 is a graph illustrating the current voltage characteristic of aninterrupted barrier-free layer of a bistable non-linear resistormaterial.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a partial schematicview is provided of the construction of a conventional picture screenmatrix with a liquid crystalline layer. The liquid crystalline layer 1is arranged between two parallel glass plates 3 and 4. Each glass platehas arranged therein a system of parallel electrically-conductivetransparent webs. Plate 3 has arranged therein a series of transparentwebs Y Y Y and Y and plate 4 a series of transparent webs X X X X and XThe electrically-conductive webs may be made of any suitable conductivematerial such as tin oxide.

FIG. 2 shows a substitute circuit diagram of the picture screen matrixconstruction shown in FIG. I. In the circuit diagram there is shown boththe capacities which are illustrated in the form of concentratedcapacities indicated by C C C,, and through C and a galvanic couplingillustrated in the form of coupling resistances indicated by r r r, andthrough r,,,,. Both the capacities and coupling resistances are due tothe conductivity of the crystalline liquid even though it may be small.If, for example, a voltage is applied to the conductor paths X and Y thecross point of these two conductor paths would be energized with thevoltage intensity developed at this cross point. This voltage intensitywould cause the corresponding cross point on the picture screen to lightup or glow. All of the remaining cross points along the respectiveconductor paths Y, and X would also receive approximately half of thevoltage of that received by the cross point of X and Y and thus showinga light-straying effect even if it is a weaker and lesser one. As can beseen from the illustrated circuit diagram, a current flow will occur,for instance, by way of the resistances and capacities, i.e. r C r; Cand r,,, C21; when the lines X and Y are energized with the exception ofthe cross point of lines X and Y Similar current flows occur at theremaining cross points.

It can readily be seen when considering the series and parallelconnections of the capacities and/or resistances which are provided bythe matrix that voltages occur at the cross points X Y X Y X Y and X Yas well as at cross points X Y X Y and X,,, Y And, as indicated, thesevoltages may be half as large as the voltage at the selected cross pointof X and Y Theoretically, the half value of energizing voltage isobtained with an infinitely large matrix. The energizing voltage will,accordingly, become lower with a matrix having a correspondingly lessernumber of X and Y lines.

FIG. 3 shows a partial section of the matrix of an indicator screenconstruction according to the present invention. In this screenconstruction, an interrupted barrier-free layer 2 of a non-linearresistor material is arranged between one of the conductor systems, i.e.the system having transparent conductor webs X X and the nematic liquidcrystalline layer 1. As can be seen in FIG. 3, the interrupted layer 2is placed directly over the individual conductive transparent webs X X Xand X, of the conductive system arranged in the glass plate 4. Such anarrangement provides a greater resistance of the voltage that may beapplied to the indicator screen matrix.

In FIG. 4, a graph illustrates the current voltage characteristic of thenon-linear resistant material of layer 2 shown in FIG. 3. According tothe present invention, when voltages are applied to the conductor pathsof the indicator screen matrix construction shown in FIG. 3 (andillustrated by the circuit diagram in FIG. 5) in such a manner that theenergizing voltage not only occurs at the intended and selected crosspoint but also in amounts of one-third of this energizing voltage at theremaining cross points, the energizing of the cross points other thanthe selected cross point can be avoided by the layer of non-linearresistor material 2 arranged between the conductor system and liquidlayer 1. This is because of the non-linear characteristics of theresistor material of layer 2 which elements are illustrated in thecircuit diagram of FIG. 5 as resistor elements R, R2 R43.

Referring to the circuit diagram shown in FIG. 5, voltage may be appliedto the conductor path X while no voltage is applied to the conductorpath Y and only one-third of the energizing voltage applied to X, isapplied to the non-selected conductor paths X X and X as well as thenon-selected conductor paths Y and Y With this arrangement, by measuringthe energizing voltage, the current-voltage characteristic of thenonlinear resistor material, and the threshold voltage of the liquidcrystalline layer 1 in a suitable manner, a lightstraying effect orglowing effect can be obtained by application of the full energizingvoltage at a selected cross point but not with the application ofone-third of the energizing voltage at the other non-selected crosspoints.

Various non-linear resistor materials may be utilized according to thepresent invention, however, aluminum oxide and tantalum oxide haveproven to be effective non-linear resistor materials in the presentinvention. Also, a cadmium selenide layer may be utilized as theresistor material 2.

As illustrated in FIG. 6 by the current-voltage characteristic of abistable resistor material, the use of a bistable layer in the presentinvention has proven to be quite advantageous. Such a current-voltagecharacteristic is shown, for example, by a cadmium selenide layer. Asindicated in the graph of FIG. 6, if a liquid crystalline layer is incontact or connected in series with a bistable layer, a low current willflow through the matrix only until a voltage is applied to the bistablelayer that exceeds a certain threshold voltage. As shown in FIG. 6,where a low voltage is applied as at the level shown by point "A", theconductivity of the bistable layer remains low and constant. However, ifthe voltage applied to the bistable element exceeds the certainthreshold voltage corresponding to point C" in FIG. 6, the conductivityof the layer increases suddenly to a level indicated by point D", i.e.greater than 1,000 times, and the liquid crystalline layer is energized.The liquid crystalline layer 2 remains energized until the appliedvoltage drops to a value represented by the point E" at which value, andpoint, the conductivity of the layer rapidly decreases to a low value asindicated by point It is preferred that a liquid crystalline matrix asprovided by the present invention have a layer ofa bistable materialsuch as cadmium selenide, inbetween the liquid crystalline layer and oneof the conductor systems. With a layer of a bistable material present inthe matrix, a positive initial voltage is applied to all Y conductorpaths, i.e., Y Y etc., and a corresponding negative initial voltage isapplied to all X conductor paths, i.e., X X etc. and the energizing ofthe desired cross point is effected in such a way that a correspondingimpulse is applied to the selected conductor paths. Accordingly, thevoltage which is applied to the selected cross point is increased to alevel that exceeds the threshold value corresponding to point C, in FIG.6, whereby the liquid crystalline layer at a location corresponding tothe cross point is transformed into a state of dynamic light-straying.

It is noted that with this arrangement it would be possible to constructa picture storer by providing a layer of a bistable current voltagematerial such as cadmium selenide in a liquid crystalline matrixprovided by the present invention. It is also noted that by including abistable material such as cadmium selenide in the liquid crystallinematrix that the selectivity of energizing a particular cross point orarea of the matrix is most easily achieved.

Although minor modifications may be suggested by those versed in theart, it should be understood that we wish to embody within the scope ofthe patent warranted hereon all such modifications as reasonably andproperly come within the scope of our contribution to the art.

We claim as our invention:

1. An indicator screen comprising two vertically superimposed systems ofparallel transparent conductor paths, a nematic liquid crystalline layerinterposed between the two conductor systems, and an interruptedbarrier-free layer of a non-linear resistor material arranged betweenone of the conductor systems and the liquid crystalline layer, saidresistor material having a high resistance where the voltage applied tothe conductor paths is less than the threshold voltage of the liquidcrystalline layer and a low resistance where the voltage applied to theconductor paths is greater than the threshold voltage of the liquidcrystalline layer.

2. An indicator screen according 0 claim 1, wherein the non-linearresistor layer is only attached to the conductor paths of the conductorsystem.

3. An indicator screen according to claim 1, wherein the non-linearresistor material consists of an oxide layer.

4. An indicator screen according to claim 3, wherein the oxide layerconsists of aluminum oxide.

5. An indicator screen according to claim 3, wherein the oxide layerconsists of tantalum oxide.

6. An indicator screen according to claim 3, wherein the oxide layerconsists of cadmium selenide.

2. An indicator screen according to claim 1, wherein the non-linearresistor layer is only attached to the conductor paths of the conductorsystem.
 3. An indicator screen according to claim 1, wherein thenon-linear resistor material consists of an oxide layer.
 4. An indicatorscreen according to claim 3, wherein the oxide layer consists ofaluminum oxide.
 5. An indicator screen according to claim 3, wherein theoxide layer consists of tantalum oxide.
 6. An indicator screen accordingto claim 3, wherein the oxide layer consists of cadmium selenide.